1. Field of the Invention
The present invention relates to data storage apparatus for magnetically reading and writing information on data storage media. More particularly, the invention concerns milliactuated suspensions designed to carry read/write heads in magnetic disk drive storage devices.
2. Description of the Prior Art
By way of background, a read/write head in a magnetic disk drive storage device (xe2x80x9cdisk drivexe2x80x9d) is typically incorporated on an air bearing slider that is designed to fly closely above the surface of a spinning magnetic disk medium during drive operation. The slider is mounted to the free end of a suspension that in turn is cantilevered from the arm of a rotary actuator mounted on a stationary pivot shaft. The actuator is driven by a rotary voice coil motor that, when energized, causes the actuator to rotate and thereby sweep the actuator arm and its attached suspension across the disk surface. By controlling the rotational movement of the actuator via the voice coil motor, the read/write head can be selectively positioned over the surface of the magnetic disk medium, allowing it to read and write data in a series of concentric tracks.
Recent years have seen an increase in TPI (Tracks Per Inch) recording density requirements in order to meet the demand for increased data storage capacity. This has necessitated greater track positioning resolution than is possible using voice coil motor control alone. One solution to the foregoing problem has been to mount a pair of small piezoelectric elements of opposite polarization to the mount plate end of the suspension. The piezoelectric elements are usually oriented in a spaced parallel arrangement, but that is not always the case. When energized, the piezoelectric elements impart small sway (i.e., across-track) displacements to the suspension. This causes the read/write head mounted at the free end of the suspension to move several tracks in either direction from its nominal position, depending on the polarity of the energy that drives the piezoelectric elements. Very fine track positioning resolution can be obtained in this fashion. Moreover, because the response time of the piezoelectric elements is generally much less than that of the voice coil motor, the seek and settle latency associated with data storage and retrieval operations can be reduced in situations where the read/write head only needs to move a few (e.g., 1-4) tracks at a time.
The aforementioned piezoelectric elements are sometimes referred to as xe2x80x9cmicroactuators.xe2x80x9d However, the term xe2x80x9cmilliactuatorxe2x80x9d is perhaps more appropriate in order to distinguish such elements from another type of electrostatic actuator that is mounted directly under, or near, the slider. This latter type of electrostatic actuator, known as a xe2x80x9cmicroactuator,xe2x80x9d has a smaller range of movement (e.g., 1-2 tracks) than the xe2x80x9cmilliactuatorxe2x80x9d elements described above. Due to their location under or near the slider, however, microactuators have better dynamic characteristics than milliactuators, which are located near the suspension hinge. The present invention concerns piezoelectric elements of the milliactuator type that are mounted in proximity to the suspension hinge.
Current disk drive suspensions tend to be about 11-18 mm in length. With the trend toward ever increasing data densities, future designs will see suspension lengths shorter than 11 mm or less. This presents a problem relative to prior art milliactuator systems. Because a disk drive suspension is normally swage-mounted to its associated actuator arm, it usually has a relatively large swage hole at its mount plate end to receive a connecting swage spud. In order to maintain adequate clearance with respect to the swage hole, the milliactuators must either be spaced longitudinally therefrom, or they must have a relatively wide lateral spacing that is in excess of the swage hole diameter. Spacing the milliactuators longitudinally from the swage hole is not a viable option in a suspension of short length. Locating the milliactuators with a wide lateral spacing is also problematic because wide milliactuator spacing means reduced sway stroke displacement at the suspension free end for a given milliactuator stroke length. A short suspension length tends to further aggravate this condition.
FIG. 1 is illustrative. It shows a suspension S that has two parallel milliactuators M1 and M2. The milliactuators M1 and M2 are spaced from each other by a distance of 2*r, where xe2x80x9crxe2x80x9d is the distance from each milliactuator to a pivot point xe2x80x9cPxe2x80x9d about which the suspension pivots due to milliactuator actuation. A distance xe2x80x9cRxe2x80x9d exists between a read/write transducer T and the pivot point P. It will be seen that the stroke length xe2x80x9cdxe2x80x9d that the milliactuators M1 and M2 must be displaced in order to achieve a sway stroke offset xe2x80x9cDxe2x80x9d at the read/write transducer T is approximated (for small angular displacements) by the relationship d=(r*D)/R. Note that an increase in xe2x80x9crxe2x80x9d or a decrease in xe2x80x9cRxe2x80x9d will result in a larger stroke length xe2x80x9cdxe2x80x9d that the milliactuators must displace to achieve a given sway stroke offset D.
One solution to the foregoing problem would be to increase the length of the milliactuators to give them a greater actuating stroke length. However, this could increase the mass and inertia of the suspension to the point of impacting one or more operational characteristics, such as the suspension""s track servoing bandwidth capability. Moreover, a longer milliactuator stroke length would introduce undesirable dynamic arm torsion bending and sway mode gains when the milliactuators are excited.
Accordingly, a need exists for a suspension design solution that facilitates the effective use of milliactuators to increase track positioning resolution in disk drive suspensions of reduced length. Preferably, this solution will not increase the mass and inertia of the suspension and will avoid introducing undesirable dynamic characteristics such as excessive gain in the suspension""s torsion and sway modes.
The foregoing problems are solved and an advance in the art is obtained by an improved milliactuated disk drive suspension assembly designed to support a transducer-carrying slider above a spinning data storage medium designed to store data in a series of concentric data tracks. According to preferred implementations of the invention, the suspension assembly includes a suspension having a mount plate, a functional end for supporting the slider, a hinge disposed between the mount plate and the functional end, and a sway compliant region on the mount plate. The compliant region is adapted to facilitate displacement of the functional end in a sway direction relative to the mount plate, such that the slider moves trackwise relative the data storage medium. A pair of milliactuators can be mounted on the suspension so as to span the compliant region. The suspension is attached via its mount plate to the arm of a pivotable actuator. The mount plate is free of swage mounting features and is secured to the actuator arm using a swageless interconnection, thus allowing the milliactuators to be closely spaced so as to improve their mechanical advantage.
In one embodiment of the invention, the swageless interconnection is provided by an adhesive bond. In an other embodiment of the invention, the swageless interconnection is provided by a snap connection. In still another embodiment of the invention, the swageless interconnection includes a damping system provided by a viscoelastic film disposed between the mount plate and the actuator arm. In yet another embodiment of the invention, the swageless interconnection is provided by the mount plate being integral with the actuator arm to provide a unimount arm configuration.
The milliactuators are preferably positioned to provide at least a ten-fold mechanical advantage between a milliactuator actuating stroke and a transducer sway stroke. The transducer sway stroke offset is preferably at least about 1 micron on each side of a nominal position of the transducer so as to provide a trackwise adjustment capability of about four tracks at 100,000 TPI (Tracks Per Inch). The milliactuators can be positioned in a mutually parallel relationship or otherwise. In a suspension having a shortened length of about 11 millimeters, the milliactuators are preferably spaced from each other by a distance of about 1 millimeter.
The invention further contemplates a method for making a suspension assembly as summarized above, and a disk drive that incorporates the suspension assembly therein.